1. Field of the Invention
This invention relates to dynamically vulcanized alloys ("DVAs") which generally comprise a polyolefin thermoplastic resin, an elastomeric component, and additives and fillers which have been added for improved chemical and physical properties.
2. Description of Information Disclosures
Polymer blends which have a combination of both elastic and thermoplastic properties are of significant commercial interest. Such thermoplastic elastomeric compositions are generally obtained by blending an elastomeric polymer with a thermoplastic resin in a way such that the elastomer is intimately and uniformly dispersed as a discrete or co-continuous phase within a continuous phase of the thermoplastic polymer. These polymer blends have been given the generic designation of Thermoplastic Olefins ("TPO"). They exhibit some of the properties of a cured elastomer as well as the reprocessability of a thermoplastic resin. The elastomeric characteristics are enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially cross-linked.
The earliest work in the curing of a TPO composition was by Gessler and Haslett; see U.S. Pat. No. 3,037,954. That patent teaches the concept of "dynamic curing" wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The resulting blend is a micro-gel dispersion of cured elastomer in an uncured matrix of resinous thermoplastic polymer.
Gessler's U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber such as, for example, butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene. Compositions of about 50 to 95 parts polypropylene and about 5 to 50 parts of rubber are disclosed.
Since these early beginnings in TPO technology, research and development has been directed towards production of TPOs having improved properties or properties desirable in a specialized application. There are several variables which may be manipulated to effect changes in the properties of TPO blends. Some of the readily apparent variables include the relative weight percentages of the elastomer and thermoplastic phases, the degree of cure of the elastomers, the composition of each of these phases, the additives and fillers used, etc.
U.S. Pat. No. 4,593,062 to Puydak et al is directed to TPOs having good flow, good physical strength characteristics, good processability, good oil resistance, low compression set and good surface characteristics in injection molded parts. The preferred embodiment of the TPO comprises equal parts of polyolefin, halobutyl rubber, and polychloroprene rubber. It is preferred that all components be present before dynamic vulcanization is initiated. However, some or all of the oil or fillers may be added after dynamic vulcanization is complete.
U.S. Pat. No. 4,735,982 to Orndorff Jr. is directed to a TPO which has low wet and dry friction and good wear resistant properties. The TPO includes additives such as oils, graphite, and glass fibers which may be added before or after the dry mixing of the thermoplastic component and the cured rubber compounds.
U.S. Pat. No. 4,130,535 to Coran et al discloses a fully cured TPO having superior tensile strength. Coran et al note that the properties of the TPOs may be modified either before or after vulcanization, by adding ingredients which are conventional in the compounding of copolymer rubber and polyolefin resin and blends thereof. In those blends utilizing carbon black as a filler, Coran et al mixes the rubber with carbon black before adding the polypropylene thermoplastic resin. Thus, the filler is present before dynamic vulcanization is initiated.
U.S. Pat. No. 4,311,628 to Abdou-Sabet et al relates to EPDM-based, phenolic cured TPOs which are tough and strong as compared to similar blends using sulfur or peroxide cures. Abdou-Sabet notes that the properties of TPOs may be modified by adding ingredients which are conventional in the compounding of EPDM rubber, polyolefin resin and blends thereof. Particularly recommended are the addition of carbon black, extender oil or both, preferably prior to dynamic curing.
U.S. Pat. No. 4,202,801 to Petersen discloses dynamically partially cured blends of monoolefin rubber, a polyolefin resin and a conjugated diene rubber. At column 5, lines 15 to 20, it states that after processing the blend, an antioxidant is added to the blend and processing is usually continued for one minute or more to incorporate the antioxidant thoroughly in the blend for the purpose of deactivating any residual curing agent and enhance protection against oxidative degradation of the composition.
U.S. Pat. Re. No. 31,518 to Fischer relates to thermoplastic partially cured blends of monoolefin copolymer rubber with a polyolefin resin. At column 6, lines 25 to 30, it discloses adding to the mixture at the end of the dynamic partial curing step a small amount of a free radical scavenging agent such as a stabilizer or antioxidant.
U.S. Pat. No. 4,217,787 to Matsuda relates to a dynamically partially cured composition comprising a peroxide curable olefin rubber, a peroxide decomposing olefin plastic and a peroxide non-curable hydrocarbon rubber and/or a mineral oil softener. At Column 9, lines 15 to 21, it states that to accelerate the decomposition of the peroxide, it is possible to use a tertiary amine or an organic metal carboxylate.
It has now been found that the addition of solid particulate fillers and certain rubber or plastic compounding additives to the thermoplastic composition after the dynamic vulcanization of the thermoplastic composition improves the stiffness to impact resistance balance of the thermoplastic composition.